1. Technical Field
The present disclosure is directed to an implant retaining device for preventing an implant from backing out of a receiving bed or graft site formed in body tissue. More specifically, the present disclosure is directed to an implant retaining device particularly suited for retaining an intervertebral implant in a receiving bed formed between adjacent vertebrae.
2. Background of Related Art
The spine is a flexible column formed of a series of bone called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The vertebrae are connected together by means of articular processes and intervertebral, fibro-cartilages.
The intervertebral fibro-cartilages are also known as intervertebral disks and are made of a fibrous ring filled with pulpy material. The disks function as spinal shock absorbers and also cooperate with synovial joints to facilitate movement and maintain flexibility of the spine. When one or more disks degenerate through trauma, spondylolisthesis or other pathologies, nerves passing near the affected area may be compressed and are consequently irritated. The result may be chronic and/or debilitating back pain. Various methods and apparatus, both surgical and non-surgical, have been designed to relieve such back pain.
One method designed to relieve such back pain is interbody spinal fusion. Typically, interbody spinal fusion involves distracting adjoining vertebrae of the spine so that the nerve root canal sizes are increased and nerve irritation is eliminated or reduced. In order to maintain the adjoining vertebrae in a distracted state, at least one intervertebral implant is inserted into a receiving bed formed in the disk space between the adjoining vertebrae. The implant is positioned to engage the adjoining vertebrae to maintain the vertebrae at a fixed degree of distraction.
Preferably, the implant should become fused to adjoining vertebrae in order to prevent the implant and adjoining vertebrae from moving. The implant must also provide spinal load support between the vertebrae. Further, during the time it takes for fusion, i.e., biological fixation of the vertebrae, to be completed, the implant should have enough structural integrity to maintain the disk space without substantial degradation or deformation of the implant.
To facilitate rapid bone growth, the implant may include or be provided with a bone growth material. The material from which the implant is constructed should be a biocompatible material and, preferably, interact biologically with the body's own naturally occurring tissues.
In order to have successful spinal fusion and maintain the stability of the spine, the vertebral implant must be fixedly positioned in relation to the adjoining vertebrae during the entire period required for fusion to occur. However, the everyday activity of a patient who has undergone a spinal fusion procedure may lead to progressive mechanical loosening and eventual failure of the implant. This significantly decreases the chances of obtaining successful fusion of the implant and the adjoining vertebrae. Therefore, it is imperative that the implant be fixedly retained in the intervertebral space during the period required for spinal fusion.
A variety of different devices have been developed to retain an intervertebral implant at a fixed position within the intervertebral space. These devices include, inter alia, screws and formations formed on the implant itself. Such devices often inhibit insertion of the implant into the intervertebral space.
Accordingly, a need exists for an improved implant retaining device which is configured to reduce the likelihood of expulsion or retropulsion of an intervertebral implant from between adjoining vertebrae during normal patient activity, without inhibiting insertion of the implant into the intervertebral space.